Purification of gases



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gr w gm gym ll go t; if i. m ems 1 ligi ihfil t RG3? GRIFFITH JONES, OE BLOGMFIELD, NEXV JEREEEY, ASSIG'NOR TO WESTINGHOUSE LAMP COMPANY, A CORPORATION OF PENNSYLVANIA.

PURIFICATION OF GASES.

2'31) ilrowiu To cZZ w 7mm 22' may concern c it known that I, Roy GRIFFITH JONES, izcn of the United States, and a resident of .olooml'ield, in the county of Essex and State of New Jerse have invented 0. new curl useful improvement in Purification of (loses, of which the following is u specificatioi i invention relates to the purification. of gas .s, and more particularly it relates to the separation of monetomic from diatomic An object the invention is the provision of a. simple, economical and rapid method for the separation rare or monutomicgases froiucomiuon or diatomic gases.

Another obiect of the im'ention is the provision of 3. process for obtaining rare or noble in it very high state of purity.

Affurther object of this invention is the provision of it process for controlling ihe de gree of purity oi" moustomic or elastic gases.

@ther will be apparent from a Feeding the specification.

is we l known that the rare gases, which exist mostly in the atmosphere, constitute such e very small percentage of the some that it is cliiiicult to obtain large quantities in very pure condition. lit is now possible to obtain the rare gases in comparatively of purity, it hit 955%, by the u of air silo. subsequent fractional sem ics of the constituents. it is also seporzii' mouotouut from the u obtain purity about passing in i xture over hide. For many purposes, such as :for use in gas-filled elecischorge devices, it

the s operctioii of the s ime thut only incuetomic and be prscticoily 3.00% pure. 11 yecuillfg' true in on electricel-clischar device which it is necessary to operate since the ionization potentials of PM rare gases are lower than those 0 mon gases.

The use of pure mouutomic gases is also valuable and necessary when it is desired to pass on electrical discharge through a. gas.

-. at a. potential less then the loniziug potential of the same; this is due to the fact ihat conduction msy take place through emonatcmic gas at the resonance potential. which is lower than the ionization, potential, whereas con .low the ionization potential.

is necessary for,

iipplication filed January 2, 1922. Serial No. 526,451.

iluction does not occur in diatomic gases be- Very small amounts, however, of common gases, when inter-mixed with the noble gases, raise the discharge potential greatly and result in ionization when conduction begins.

A hot-ccthode gas-fille l rectifier is an example of a device which it-is necessary to operate below the ionization potential of the gas because, if operated at or above this potential, positive ions bombard the hot cathode and destroy it. This would be the case if a. very small percentage of ztdiatomic gas were present, since this gas would be ionizecl. However, by using a substantially pure monetomic gas, the discharge can take place without substantial ionization and, consequently, without deterioration of the cathode.

For the separation of the monatomic from the diatomic ases, I employ reagents which are capable or combining with the diatomic or common gases and which form therewith reaction products having a negligibly low rapid purification heat the re igcnt to, u

comparatively high t inpora turc to activate it, complc e purification. cannot be obtained by kccpiu the. reugeit at this temperature. I have .iouml, however, that rapid and complete piuificstion may be eii'ected by reduo ing the temperature of the reagent whilecoutinuing the circulation of the gases in contact therewith. I have found also that flier-e is a definite relation between the temperature to which the reagent is cooled while circulating the gas and the purity of the letter, iLlfi iurity increasing as the temperatureof the reagent (lo-creases. (hie csuse for this may be that the dissociation of the reaction products is less at low than at high temperatures, so that there-is less re-coutermination of the gas at the low temperature.

The reagent used to purify a monatomic gas may be any solid which requires heating above room teu'ipcraturc to activate it and which will react with the impurity to be eliminated to form solid compounds of low vapor pressure atreducccl temperatures.

Since it is frequently necessary to eliminate several impurities from a monatomic gas, any required number of purifying agents may be used, either simultaneously or in succession, each agent being selected as the best eliminaut of a given impurity. I have found it convenient, however, to use metals, such as barium, strontium, magnesium and calcium, which combine with and fix all the diatomic gases commonly found in the rare gases. Calcium is especially valuable in this Way as it reacts rapidly with every gas having valency, that is, with all gases except those of the zero group of the periodic table, to form solid compounds. For the purpose of simplicity and illustration, therefore, discussion of the purifying agent will be'restricted to calcium.

In the separation of nitrogen, for example, from a monatomic gas, such as argon,

it is found that it is necessary to heat the calcium to a temperature in the neighbon hood of 700 in order to start the reaction With nitrogen, but it is also found that the argon cannot be obtained in its highest state of purity if repeatedly passed over calcium at its reaction temperature. The reason for this is probably due to the fact that, while the calcium combines with impurities at this temperature, the reaction is reversible, or, in other words, the reaction products are partially dissociated at "the activation temperature so that there is always present in the gas small amounts of im urities which are released by association. This may be illustratedby the equation:

The nature of the reaction between calciurnand nitrogen is such that it does not proceed completely to the right at high temperatures, the calcium nitride slightly decomposing which causesfthe reaction to go to the left.

- When water vapor, for example, as well 'as nitrogen, is to be separated from the Elli gases while the calcium is slowly coo ed, a

till

,monatomic gases, the maintenance of the very pure monatomic gas'ie obtained.

If a monatoniic gas containing definite amount of a diatomic gas is ole-aired, the temperatme of the calcium be brought down to the temperature correspondip to the degree of urit desired... As an illustration of the ene cial action efthe gradual cooling of the calcium, the following escapee table is submitted showing the relation of temperature to purity.

Temperature Arc drop of furnace. n argon.

The percentage purity of the gas, however, (argon in this case), is not stated directly in this table, but a function of the purit Y is shown. age rop in the arc of a hot-cathode device in which the discharge passes through a monatomic gas combined with small amounts of impurities. It is found that the arc drop in such a device is a function of the purity of the gas through which the discharge passes, the: arc drop becoming less the purer the mo'natomic gas through which the discharge passes. F or example, an arc drop of 7 volts will indicate a purer gas than an arc drop of 13 volts measured under the same conditions of gas pressure, cathode temperature, distance of the anode from the cathode, current through the device,-materials of the electrodes, etc.

It will be noted from the table that the gas becomes purer and lower the temperature to which the calcium is brought While passing the gas to be purified continuously over it. By cooling the calcium below room temperature, it is possible that such action may lead to a still further increase in purity, although it is found that WIIIOIlfitOlHlQ gas, practically 100% pure, as shown by the spectroscope, can be obtained by cooling the calcium to room temperature.

In practicing this invention, the calcium is preferably placed in a divided condition in nickel tubes or boats, which are placed inside closed steel tubes which, in turn, are placed in a furnace and heated to the required temperature. It is found that this method for separating the common from the rare gases enables me to purify a large quantity of gas. in a "very short period of time and to effect a complete separation of the inonatoznic from the diatomic gases.

Minor modifications may readily be made in the process as above described to attain the same results, but it is to be understood.

that such modifications come within the scope of this invention, as embraced in the appended claims.

V hat is claimed l. The step in process of separating This function is the volt-- till 

